The present invention relates generally to reproducing of a record carrier using magnetic means, and more particularly to a magnetoresistive device. The present invention is suitable, for example, for a read head, a magnetic sensor, a magnetic switch, etc. for use with a hard disc drive (referred to as “HDD” hereinafter).
Available electronic information content has been explosively increasing with the recent rapid technology development, as in the Internet. Accordingly, smaller and larger-capacity magnetic recorders, typified by HDDs, have been increasingly demanded to store such a large amount of information. A surface recording density indicative of recordable information content per unit recording area is required to be higher to realize a smaller and larger-capacity HDD.
The increased surface recording density accordingly reduces an area on a record carrier corresponding to one bit as a minimum unit of magnetic record data, and a signal magnetic field from the record carrier becomes weaker as a matter of course. A small and highly sensitive read head is required to faithfully read such a weak signal magnetic field with certainty.
It is expected that the surface recording density of 100 Gbit/inch2 would generally requires a recordable track width of about 0.1 μm on the carrier. Currently available read heads having a spin-valve device use a so-called Current in Plane (referred to as “CIP” hereinafter) configuration that applies the sense current parallel to laminated surfaces in the spin-valve device. With higher surface recording density, a read head size should be reduced according to a reduced bit size. This is because a read head excessively large for a record bit size would simultaneously take in magnetic information from both a target record track and track(s) adjacent to the target record track, deteriorating resolution in a direction of track's width. Reading of magnetic information on a track that has been recorded with the surface recording density of the 100 Gbit/in2 would require a read core width with a size of 0.1 μm or less, and this very precise process accuracy is one cause that hinders an implementation of the read head.
A tunneling magnetoresistive head (“TMR head” hereinafter), which has currently been developed as a high output head flows the sense current in a direction perpendicular to the core width, and thus the resistance value increases in reverse proportion to the core width. Since an available current value becomes small in the TMR head with a large resistance value, a read electric signal easily contains noises and makes difficult the implementation of the highly sensitive TMR head.
A flux guide type read head has been proposed as one solution for these problems. The flux guide type read head structurally forms such a flux guide between a reading surface and a device, such as a spin-valve device and a TMR device, that the flux guide facilitate reading by taking the magnetic flux from the carrier and transmitting it to the device, for example, a free layer in the spin valve. As the flux guide structure defines a core width as a flux guide's width and the core width does not depend upon the size of the device, the flux guide structure may advantageously maintain a larger device size relative to the track width and mitigate the process accuracy required for the device.
The conventional flux guide requires a thickness of at least about 20 Å in order to change a direction of magnetization of the device and to maintain the uniform magnetic property for the entire magnetic film. Therefore, the demagnetizing field that increases in proportion to the thickness at a film end face prevents the flux reversal in the flux guide. As a result, this disadvantageously drastically decreases the magnetic flux transmitted to the device, such as a free layer in the spin valve device, and lowers the sensitivity of the head. There is another problem in that the magnetic field in proportion to the thickness is formed around the flux guide and deforms the adjacent device, such as the free layer in the spin valve.